1. Field of the Invention
The present invention relates to a printing apparatus that is capable of estimating an amount of ink available for supply to a printing head, and a method for estimating an amount of ink.
2. Description of the Related Art
In recent years, in the field of printing apparatuses, such as printers, copiers and facsimiles, an ink-jet printing system employing a printing head capable of ejecting minuscule droplets of ink in response to a high-frequency driving signal has been widely used. In an ink-jet printing system which requires a user to replace an ink tank, it is important to notify the user of depletion of the ink in the ink tank. Especially, for devices, such as facsimiles, which do not allow transmitted data to be kept by a user, it should be avoided to perform a printing operation with no ink being ejected from the printing head (empty printing) due to depletion of ink. For this reason, it is desired to enhance the accuracy in estimating an amount of ink available for supply to the printing head (hereafter also referred to as “remaining ink amount”).
Japanese Patent Laid-Open No. Hei 03-259662 discloses a method for estimating a remaining ink amount on the basis of the temperature of a printing head and the value of a current flowing through the printing head. Japanese Patent Laid-Open No. Hei 07-032608 discloses a method for estimating a remaining ink amount on the basis of vibration of a vibration plate which is being sprayed with ink. Japanese Patent Laid-Open No. Hei 09-094947 discloses a method for estimating a remaining ink amount on the basis of a change in the current value caused when ejected ink is passing between optical elements. The common point among these methods is to detect whether or not ink has actually been ejected from a printing head by using some method while causing the printing head to operate in response to a signal instructing the printing head to eject ink. Moreover, another common point is to determine that the remaining ink amount is zero when ink is not ejected from the printing head. Being capable of detecting whether or not ink is actually ejected from the printing head, these methods for estimating an amount of ink achieve high accuracy in estimating a remaining ink amount.
However, although a remaining ink amount can be estimated with high accuracy in these methods, it is required that ink be actually ejected from the printing head in order to estimate the remaining ink amount. As a result, the amount of ink available for printing is reduced by that consumption needed for the estimation process.